Electrical systems in residential, commercial and industrial applications usually include a panelboard for receiving electrical power from a utility source. The electrical power is then delivered from the panelboard to designated branch circuits supplying one or more loads. Typically, various types of protective devices are connected to the branch circuits to reduce the risk of injury, damage or fires, The protective devices may be mounted within the panelboard or external to the panelboard.
Circuit breakers are a well known type of protective device which are designed to trip open and interrupt an electric circuit in response to detecting overloads and short circuits. Overload protection is provided by a thermal element which, when heated by the increased current, will cause the circuit breaker to trip and interrupt the power. This can occur when too many loads draw power from the same branch circuit at the same time, or when a single load draws more power than the branch circuit is designed to carry. Short circuit protection is provided by an electromagnetic element that trips when sensing high current flow. Additionally, many circuit breakers include ground fault interruption (GFI) circuitry to protect against ground faults which occur when current flows from a hot conductor to ground through a person or object.
Arcing fault detectors are another type of protective device which may be employed in an electrical distribution system. Arcing fault detectors are designed to trip open and interrupt an electric circuit in response to arcing faults, which occur when electric current "arcs" or flows through ionized gas between two ends of a broken conductor, between two conductors supplying a load, or between a conductor and ground. Arcing faults typically result from corroded, worn or aged wiring or insulation, loose connections, wiring damaged by nails or staples through the insulation, and electrical stress caused by repeated overloading, lightning strikes, etc. The presence of an arcing fault creates a significant fire hazard because it generates heat which may ignite the conductor insulation and adjacent combustible materials. Standard circuit breakers typically can not detect arcing faults because branch or load impedance may cause the level of load current to be reduced below the trip curve setting of a standard circuit breaker.
Each branch circuit of the electrical distribution system may include a selected combination of standard circuit breaker components, arcing fault detection circuitry or GFI circuitry to protect the branch circuit from associated hazardous conditions including overcurrents, arcing faults and ground faults. Whatever combination is selected, it is preferred that the protective devices are packaged together within a miniature circuit breaker housing adapted to be positioned within an electrical distribution panelboard or load center.
The present invention relates to the production of circuit breakers including arcing fault detection components in conjunction with standard circuit breaker components and/or GFI. Production of such circuit breakers by automated equipment is desirable. Consequently, the present inventors have sought improved arcing fault detectors which facilitate automated production, or, if desired, manual assembly, through "top-down" methods, which require access from only one side of the circuit breaker.